uss/gluster: creating file/directories inside .snaps should fail with
EROFS

When an attempt is made to create file/directories inside .snaps, it
fails with wrong error message as "Stale file handle". It should fail
with "Read-only file system"

Change-Id: I3a812a0afc4762cbb71ab180b9394c866e576a66
BUG: 1159840
Signed-off-by: vmallika <vmallika@redhat.com>
Reviewed-on: http://review.gluster.org/9039
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>